飞秒时间分辨实验中相关函数和时间零点的确定

Determine the cross correlation function and the zero of time of the pump and probe laser in femtosecond time-resolved studies

结合飞秒激光在研究分子激发态弛豫动力学中的应用,介绍了几种飞秒时间分辨实验中确定泵浦激光脉冲与探测激光脉冲的相关函数和时间零点的方法.对于波长在可见波段的泵浦和探测激光脉冲,我们可以利用非线性光学的技术手段,探测泵浦光与探测光的和频光的强度随二者间的时间延迟的变化来确定相关函数和时间零点;对于波长在紫外甚至更短的波段的泵浦和探测激光脉冲,由于单脉冲能量比较低,目前还很难利用技术手段来测定泵浦激光与探测激光的相关函数及时间零点,可以利用某些原子气体(如Xe)或某些具有短寿命态的分子作平行实验进行间接测量.

By presenting the examples of applying the femtosecond pump-probe technique to study the relaxation dynamics of the molecular excited states, introduced several methods to determine the cross correlation function as well as the zero of time of the pump and probe laser pulse in femtosecond time-resolved experiments. For the pump and the probe laser pulses in the visible light range, we can make use of the non- linear optical technique to detect the transient of the intensity of the second harmonic generation with the delay time of the pump and the probe pulses, the second harmonic generation of the pump and the probe laser pulses is produced by a BBO crystal. Due to the low pulse energy, there are as yet no established techniques for the determination of such correlation function as well as the zero of time for the ultrafast pulses in the UV or the VUV. Calibration method by use of the ionization signal of some atom gas such as Xe or some short life-time molecules would be an ideal method.